50: Supercritical Fluid Extraction of Compounds from Microalgae and Aromatic Plants

Recently, there has been an increase in public awareness on the health, environmental and safety hazards associated with the use of toxic organic solvents in food processing. The high cost of organic solvents, the increasingly stringent environmental regulations and the new requirements from the medical and food industries for ultrapure and high-added-value products have pointed out the need for the development of new and clean technologies for the processing of food products. On the other hand, the 12 principles of green chemistry emphasize the importance of sustainable processes, which minimize waste generation and energy consumption. The compliance of these concepts will lead to a cleaner environment and a more cost-effective use of resources. Thus, the solution passes by the development of more sustainable technologies that significantly increase the efficiency of chemical processes and reduce the operation time of such technologies. Conventional extraction techniques for solid vegetable matrices include Soxhlet, hydrodistillation, shake-flash methods, maceration and pressing. These methods present many disadvantages since they use toxic solvents, with the associated risks for human health and the environment, are time consuming, labor-intensive, present low yield and selectivity, and have high energy consumption. Therefore, the design of green, efficient and sustainable extraction techniques is mandatory. Thus, the green extraction processes should consider the minimization of the use of toxic solvents, reduce waste production, avoid the presence of toxic solvents in the final product and lower the energy consumption of the processes. Among the several techniques complying with these requirements, supercritical fluid extraction (SFE) is considered one of the most suitable for the extraction of compounds from vegetable matrices. Supercritical CO₂ extraction has provided an excellent alternative to the extraction and isolation of valuable compounds from natural products. In this section, SFE studies of compounds from microalgae and aromatic plants are described in more detail. Some of the most interesting experimental results obtained at the Experimental Thermodynamic Laboratory at the Technical University of Lisbon are presented and discussed.